Previous immunoblotting studies have demonstrated IgG directed against VPl of human rhinovirus serotype 2 (HRV2) in the sera of all adults tested, but no correlation exists between neutralizing antibodies and immunoblot binding antibodies. In order to further study the interaction, sera from pediatric patients in the United States and Chile were examined, and sera from guinea pigs with monospecific neutralizing antibodies were tested in the immunoblot system. Adult sera were studied for the antibody isotype and subtype. HRV2 replicated in WISH human amnion cells, purified on CsC1 gradients, separated into the major individual structural capsid proteins (VP1, VP2, and VP3) by electrophoresis on polyacrylamide gels, and transblotted onto nitrocellulose was prepared for immunoblots. With few exceptions (1/23 from the U.S. and 4/79 from Chile) the tested pediatric sera reacted with VP1. Some sera also had antibody to VP2 and VP3 but a smaller percentage than noted with adult sera. Monospecific guinea pig neutralizing antisera against a variety of HRVs indicated cross reactive binding against VPl of HRV2 in the immunoblot system. Immune guinea pig sera reduced but did not completely eliminate binding of human sera to VP1. Guinea pig antisera did not bind to VP2 or VP3, and did not compete for binding of human IgG to VP2 and VP3. Adult sera demonstrated concentration dependent binding of antibodies to VPl for IgG, IgA, and IgM. The IgG antibodies were predominantly IgGl and IgG3 with little or no IgG2 or IgG4. The data suggest that antibodies which bind to HRV peptides are present widely from childhood but increase in concentration and number of peptides recognized as age increases. The cross reactivity of guinea pig sera suggests that many HRVs share epitopes that could serve as the basis for another system of grouping. The incomplete competition of human and guinea pig sera suggests recognition of some identical and some unrelated epitopes on the viral capsid.